1) Field of the Invention
The present invention relates to a corrugator and corrugated fiberboard sheet manufacturing method for bonding a front (front-side) linerboard, a corrugating medium and a rear (rear-side) linerboard together to manufacture a corrugated fiberboard sheet.
2) Description of the Related Art
FIG. 11 is a side elevational view schematically showing a prior common corrugator.
As shown in FIG. 11, a prior common corrugator is mainly composed of single facers A1, A2, a double facer B, a dry end C comprising a slitter scorer, a cut off (or cutter), a stacker and others, and a stacking or storage section D.
First, the single facers A1, A2 receive base corrugating mediums a1, a2 to shape them into a corrugated configuration and subsequently adhere them to rear-side base linerboards b1, b2 introduced thereinto in a different way, thereby producing a single faced corrugated fiberboard sheet. At this time, for setting or solidifying a starch paste used, the base corrugating mediums a1, a2 are respectively heated by preheaters d1, d2 while the rear-side base linerboards b1, b2 are respectively heated by preheaters c1, c2.
The single faced corrugated fiberboard sheet thus produced, together with a front-side base linerboard f, is heated by a preheater e, and then, is introduced through a gluing unit g into the double facer B.
This double facer B is, as shown in FIG. 12 being a side elevational view schematically showing a more detailed structure, made up of a group of heating plates h located at its lower section, a pressurizing unit i disposed above the group of heating plates h to be in opposed relation thereto for pressing a rear surface of a belt through the use of an air pressurizing device, a weight roll or the like to pressurize a single faced corrugated fiberboard sheet 4 and a front linerboard 1, and upper and lower conveyers j, k for holding and conveying a double faced corrugated fiberboard sheet 5 being an adhered assembly sheet made by the adhesion of the single faced corrugated fiberboard sheet 4, formed in a manner that a rear linerboard 2 is joined onto a corrugated medium 3 shaped into a corrugated configuration, to the front linerboard 1.
In addition, in the double facer B, the single faced corrugated fiberboard sheet 4 and the front linerboard 1 introduced between the group of heating plates h and the pressurizing unit i are situated to be adhered through a glue, attached onto the flute tip portions of the corrugated medium 3 of the single faced corrugated fiberboard 4, to each other, and the front linerboard 1 receives the heat from the group of heating plates h while sliding and traveling in a contacting condition with the group of heating plates h, so that its temperature raised thereby serves as heat to solidify the starch paste, thus manufacturing the double faced corrugated fiberboard sheet 5. The double faced corrugated fiberboard sheet 5 produced by the adhesion in this way is conveyed through the upper and low conveyers j and k to be outputted into an after-processing section including a slitter scorer 1 and a cut off m as shown in FIG. 11.
Subsequently, as shown in FIG. 11, in the dry end C, the double faced corrugated fiberboard sheet 5 outputted thereinto is slitted and ruled by the slitter scorer 1 and, further, is cut by the cut off m to be processed into divided corrugated fiberboard sheets each having a given or predetermined configuration. Further, as shown in the more-detailed side-elevational view of FIG. 13, after being conveyed by a stacker n, the double faced corrugated fiberboard sheets 5' thus divided are stacked in the stacking section D and then carried out to the external.
Meanwhile, in the case of such a prior corrugator, since the starch paste used as an adhesive is solidified to produce an adhesive force, the preheaters c1, c2, d1, d2 and e are located to heat the rear linerboard 2, the corrugated medium 3 and the single faced corrugated fiberboard sheet 4 being the adhered assembly sheet comprising the rear linerboard 2 and the corrugated medium 3, respectively. In addition, the group of heating plates h are placed to adhere the front linerboard 1 to the single faced corrugated fiberboard sheet 4 by heating from both the front linerboard 1 side and rear linerboard 2 side.
Thus, in the case of this prior corrugator, since the respective sheets are heated in its first half section, the temperature of the sheets heated is kept even in its second half section, with the result that the divided double faced corrugated fiberboard sheets 5' are stacked in the stacking section D in a dried condition assuming a considerable high temperature and low moisture.
For instance, in the divided double faced corrugated fiberboard sheets 5' immediately before stacked in the stacking section D, the moisture content on the front linerboard 1 side reaches approximately 3 to 4% while the moisture content on the rear linerboard 2 side comes to 4 to 5%, thus making a difference in moisture between the front linerboard 1 side and the rear linerboard 2 side.
Furthermore, it takes approximately several tens hours until the divided double faced corrugated fiberboard sheets 5' stacked in the stacking section D reaches the equilibrium moisture (for example, 7 to 9%), in the meantime, the front linerboard 1 and rear linerboard 2 of each of the divided double faced corrugated fiberboard sheets 5' produce moisture distributions in their planes, respectively.
FIG. 14 is an illustration of the measurement results of moisture variation in a surface circumferential section and surface central section of the front linerboard 1 or rear linerboard 2 which occurs from when they are stacked in the stacking section D until reaching the equilibrium moisture in terms of the divided double faced corrugated fiberboard sheets 5' manufactured by a prior corrugator.
In FIG. 14, as indicated by a broken line, the surface circumferential section of the front liner 1 or the rear linerboard 2 tends to absorb the moisture from the atmosphere and, hence, reaches the equilibrium moisture in approximately several hours, whereas, as indicated by a solid line in the same illustration, the surface central section of the front linerboard 1 or the rear linerboard 2 does not tend to absorb the moisture from the atmosphere and, from this reason, reaches the equilibrium moisture in approximately several tens hours because the moisture content slowly increases.
Thus, since the times taken until reaching the equilibrium moisture differ from each other to make the difference in moisture, the extension quantity of the surface circumferential section of the front linerboard 1 or the rear linerboard 2 exceeds the extension quantity of the surface central section thereof. For this reason, difficulty is experienced to maintain the plane condition of the front liner 1 or the rear liner 2, so that buckling deformation occurs, which causes warp deformation with the passage of time as shown in FIG. 15 showing a stacked condition to make it difficult to improve the quality of the double faced corrugated fiberboard sheets 5'.
Taking into consideration the passage-of-time warp deformation occurs because of the difference in moisture between the front linerboard 1 and rear linerboard 2 of the stacked double faced corrugated fiberboard sheets 5' and the passage-of-time difference in moisture between the surface central section and surface circumferential section of the stacked front linearboard 1 or rear linerboard 2 as mentioned above, there has been proposed a sheet wetting apparatus (see Japanese Patent Laid-Open (kokai) No. HEI 8-34081) which can reduce such differences in moisture.
Referring to FIG. 16, a description will be made hereinbelow of this sheet wetting apparatus.
This sheet wetting apparatus is, as shown in FIG. 16, composed of moisture sensors 14s, 14r placed on the downstream side of the upper and lower conveyers j, k, spray units (which are, in this case, for supplying water, and therefore, referred hereinafter to as water spray units) 6s, 6r provided on the further downstream side of the moisture sensors 14s, 14r for the supply of a liquid (for example, water), liquid (water) quantity adjusting units 16s, 16r respectively coupled to the spray units 6s, 6r for adjusting the flow rates of the supply liquid (in this case, water) thereto, a controller 17, a presetting unit 18, and an integrated control system (production management system) 19.
The moisture sensors 14s, 14r measure the moisture contents of the front linerboard 1 side and rear linerboard 2 side of the double faced corrugated fiberboard sheet 5 on the downstream side of the upper and lower conveyers j, k, while the controller 17 calculates an undermoisture quantity (the shortage of moisture quantity) with respect to a desired or target moisture (desired moisture value) on the basis of the outputs of the moisture sensors 14s, 14r, and further, calculates a lacking supply liquid flow rate corresponding to the calculated undermoisture quantity to adjust the flow rate of the supply liquid by the water quantity adjusting units 16s, 16r on the basis of the calculated lacking supply liquid flow rate, thereby accomplishing the sheet wetting with the adjusted supply liquid quantity through the use of the water spray units 6s, 6r.
Furthermore, the above-mentioned publication says that this sheet wetting apparatus is designed such that, if the physical properties depending on the paper quality can be grasped in advance with no use of the moisture sensors 14s, 14r and the operating condition of each portion of the corrugator is monitored so that the movement or status of the front linerboard or the rear linerboard on the line is estimable, the production management system 19, which integrally manages these known data and the monitored information, gives set values to the presetting unit 18 for the integral control of the water quantity adjusting units 16s, 16r.
However, the method of using this sheet wetting apparatus and of conducting the sheet wetting operation at the positions of the water spray units 6s, 6r can not accurately achieve the moisture supply adjustment to the sheet. That is, if the moisture supply quantities by the water spray units 6s, 6r vary to make it difficult to adjust the sheet moisture to the desired moisture, difficulty is encountered to directly detect the sheet moisture after the moisture supply, thus resulting in inaccurate moisture supply quantity to the sheet.
Still further, although, as mentioned above, the above-mentioned publication says that this sheet wetting apparatus is made such that, if the physical properties depending on the paper quality can be grasped in advance with no use of the moisture sensors 14s, 14r and the operating condition of each portion of the corrugator is monitored so that the movement or status of the front linerboard or the rear linerboard on the line is estimable, the production management system 19, which integrally manages these known data and the monitored information, gives the set values to the presetting unit 18 for the integral control of the water quantity adjusting units 16s, 16r, there is no detailed description about the paper physical properties and operating conditions to be actually taken therefor.
Moreover, a description will be taken hereinbelow of a sheet wetting apparatus with another construction. This sheet wetting apparatus is, as shown in FIG. 17, made up of moisture sensors 14s, 14r provided on the downstream side of the upper and lower conveyers j, k, water spray units 6s, 6r located on the upstream side of a pressurizing unit i and the group of heating plates h for giving a supply liquid (for example, water), liquid (water) quantity adjusting units 16s, 16r communicated with these water spray units 6s, 6r, a controller 17, and an integrated control system (production management system) 19.
The moisture sensors 14s, 14r measure the moisture contents of the front linerboard 1 side and rear linerboard 2 side of a double faced corrugated fiberboard sheet 5 on the downstream side of the upper and lower conveyers j, k, while the controller 17 calculates an undermoisture quantity with respect to a desired moisture on the basis of the outputs of the moisture sensors 14s, 14r, and further, calculates a lacking supply liquid flow rate corresponding to the calculated undermoisture quantity in order to control the flow rate of the supply liquid by the water quantity adjusting units 16s, 16r on the basis of the calculated lacking supply liquid flow rate, thereby accomplishing the sheet wetting with the adjusted supply liquid quantity through the use of the water spray units 6s, 6r.
In this case, the integrated control system 19 can emit the paper physical property data to the controller 17 so that the flow rate is adjustable while taking this data into consideration.
However, if the humidification for the sheet takes place at the positions of the water spray units 6s, 6r as mentioned in this sheet wetting apparatus, the moisture supply takes place before the adhesion between a single faced corrugated fiberboard sheet 4 and a front linerboard 1, and therefore, the adhesion therebetween is done in a state where the extension quantities thereof vary, which rather causes the upward and downward warps.
In addition, although the integrated control system 19 sends the paper physical property data to the controller 17 so that the flow rate is adjustable while taking this data into consideration, there is no concrete description about the paper physical property data to be taken into consideration.
Moreover, a description will be made hereinbelow of a sheet wetting apparatus with a different construction. This sheet wetting apparatus is, as shown in FIG. 18, designed to humidify a belt of an upper conveyer j' by a water spray unit 6s and further to humidify a belt of a lower conveyer k by a water spray unit 6r to supply moisture to a front linerboard 1 side and rear linerboard 2 side of a double faced corrugated fiberboard sheet 5 through the belts thus humidified.
However, the moisturizing method based upon such a sheet wetting apparatus can not sufficiently humidify the sheet and can not perform the fine control of the moisture supply quantity.
Meanwhile, although the prior corrugators are designed such that, in the double facer B, the pressurizing unit presses a rear surface of a belt through an air pressurizing device, a weight roll or the like to pressurize the single faced corrugated fiberboard sheet 4 and the front linerboard 1, it has been proposed that, in order to improve the quality of the double faced corrugated fiberboard sheet 5, a plurality of pressurizing units are separately disposed along the sheet conveying direction.
However, in the case of a double facer with such pressurizing units, since the pressurizing units are disposed in a separate condition to make a single faced corrugated fiberboard sheet 4 and a front linerboard 1 (a double faced corrugated fiberboard sheet 5 is produced when they are adhered to each other) susceptibly exposed to the outside air so that the function to remove the moisture from the single faced corrugated fiber sheet 4 and the front linerboard 1 improves, the double faced corrugated fiberboard sheet 5 existing on the immediate downstream side of the double facer has a tendency to have a high temperature and a low moisture. For this reason, the moisturizing method based upon the above-mentioned sheet wetting apparatus can not accomplish the sufficient humidification for the sheet and can not conduct the fine control of the moisture supply quantity, and therefore, difficulty exists in certainly suppressing the warps of the sheets occurring with the passage of time.